Glow-discharge display device

ABSTRACT

Electrical glow-discharge display device with an array of glowdischarge paths and a cross-bar addressing system therefore. Each anode of a row is, through an electrically resistive connection, connected to a common row supply conductor. The anodes, the electrically resistive connections and the row supply conductors are formed by thin films on a face plate of the device. An insulating layer covers the thin films with the exception of breaks at each anode film.

Oct. 9, 197 3 GLOW-DISCHARGE DISPLAY DEVICE Inventor: James Smith, Salfords, England Primary ExaminerRoy Lake Assistant ExaminerDarwin R. l-lostetter Att0rneyFrank R. Trifari [73] Assignee: U.S. Philips Corporation,New York, N.Y.- [22] Filed: June 28, 1972 {57] ABSTRACT [21] Appl. N0.: 267,141

0 Electrical glow-discharge display device with an array [30] Fore'gn Applicauon Prlomy Data of glow-discharge paths and a cross-bar addressing July 22, I971 Great Britain 34,369/71 system therefore. Each anode of a row is, through an 7 electrically resistive connection, connected to a coml Cl mon row supply conductor. The anodes, the electri- 1 5/ cally resistive connections and the row supply conduc- [5 l Int. Cl. H01j 7/44 tors are formed by thin films n a fa plate f th 1 [58] Field of Search 313/210, 220; vice. An insulating layer covers the thin films with the 71 exception of breaks at each anode film.

[56] References Cited 7 Claims, 3 Drawing Figures UNlTED STATES PATENTS 3,334,269 8/l967 LHeureux 315/5 8 l 14 11 U w t I 10- 1 I" 12 1 12 15- I L PATENTED 9 75 SHEET 2 BF 2 14 Algm/ v% Allll GLOW -DISCHARGE DISPLAY DEVICE The invention relates to an electrical glow-discharge display device comprising an array of anode-cathode electrode pairs defining an array of individually addressable glow-discharge paths through a gas atmosphere contained in said device,-and a cross-bar addressing system therefore, the anodes of each row of the array being individually connected through an electrically resistive connection to a common row supply conductor which forms part of the addressing system.

Such a device may be used for displaying simple patterns such as diagrams, numerals, words or the like. Energisation of the individual discharge paths in such devices may be accomplished by supplying each one separately from an external circuit. Thus the device may include a common anode for all the elements and individual connections to each cathode. While this is feasible'for small total members of elements e.g., a 7 X array, for larger arrays the required number of individual connections to the device rapidly becomes impracticably large and it becomes necessary to use an alternative form of addressing each element, such as a cross-bar addressing system in which an element is energised only during the period in which the row and column containing that element are energised.

In a typical embodiment of this the cathodes are connected together in linear groups, say in columns, and the anodes are connected together in a linear groups orthogonal to these, say in rows. (The terms row and column are used herein namely in a comparative sense; in practice the array may be orientated so that the rows extend from top to bottom and the columns extend from side to side.) A current limiting resistor is connected in series with each anode row or each cathode column in order to limit the current through the discharges. As each current limiting resistor can control only one discharge at any time the resistor must be time-shared between all the discharges on its row or column. Thus if the current limiting resistors are in the cathode columns the anode rows must be switched on in a cyclic manner. If there are n rows a discharge cannot be operated for a time greater than a fraction lln of the total time. (In practice the maximum operating time of each discharge will be even less than this because of its finite switch-on time). This mode of operation has the disadvantage that, whilst operating, each discharge must give out at least n times the mean light output required. The cycling time must also be sufficiently rapid to avoid a flickering effect from the display.

One way of overcoming this is to arrange that each element stays on, once it has been energised, until an of pulse is applied thereto. This is theoretically possible because, once a discharge has been initiated, the voltage necessary to maintain that discharge is lower than that required to initiate it. Thus, if the row and column conductors are maintained at a relative potential difference which is greater than the maintaining voltage for the discharge but less than their striking voltage, all elements will remain off until the voltage between the row and column conductor corresponding to a particular element is momentarily raised to above the striking voltage. When this is done the element in question will strike, and moreover it will remain on after the momentarily raised voltage has returned to its initial value. Thus successive elements can be energised in turn, and will remain on unless steps are taken to subsequently extinguish them. This can be done by momentarily reducing the voltage between the row and column conductor corresponding to a particular element.

There is one major problem which arises if energising a device in this way is attempted. The current-limiting resistors cannot be time-shared as in the cyclic mode of operation described above. One resistor must be permanently connected in series with each display element either in the anode or in the cathode lead thereto. This is fairly easy to do when either all the individual anodes or, as in display tube type 1251 obtainable under the Registered Trade Mark Mullard, all the individual cathodes have separate external connections, but in a panel having many display elements this is difficult and in such a case it is advantageous to include the individual resistors within the panel itself.

An electrical glow-discharge display device is known (see U.S. Pat. 3,612,938) with an electrically resistive layer consisting of a phosphorus vanadate glass on the anode conductors of a cross-bar addressing system in a glow-discharge display tube. Thus the current to an individual discharge must pass through the corresponding portion of the resistive layer, this layer effectively providing a separate resistor in series with each discharge.

It is an object of the present invention to provide an alternative way of providing individual series-resistors.

An electrical glow-discharge display device of the type mentioned in the preamble is, according to the invention, characterized in that the anodes, the electrically resistive connections and the row supply conductors are formed by thin films deposited on an inner surface of an optically permeable viewing window of the device, and that at least the major portion of the electrically resistive connections and of the row supply conductors are covered with an electrically insulating layer.

Thin-film" is to be understood herein to mean an electrically conductive or semiconductive film which has been deposited in a vacuum or a reduced-pressure atmosphere.

The insulating layer is preferably substantially continuous over substantially the whole of said inner surface with the exception of breaks at each anode film.

In a preferred embodiment of the invention is characterized in that an individual electrically conductive layer is deposited over the insulating layer which covers each electrically resistive thin-film connection, and that said conductive layer electrically contacts the cor responding anode film.

Preferably each said electrically resistive connection comprises a meandering path of a film of an electrically resistive material.

Said electrically resistive material is preferably nichrome and said anodes and said row supply conductors are preferably formed by a nichrome film which is thicker than the film forming said electrically resistive connections.

Another preferred embodiment according to the invention is characterized in that the cathodes and column supply conductors therefore comprise elongate electrical conductors which extend through a block of electrically insulating material so that each elongate conductor is exposed at the base of each cavity of a column of cavities in a major surface of said block, the

inner surface of said viewing window facing said major surface with the anode films aligned with the open ends of the cavities and spaced therefrom.

Each cavity preferably tapers from its open end to its base.

An embodiment of the invention will be described, by way of example, with reference to the accompanying drawing in which:

FIG. 1 is a plan view of part of a glow-discharge display tube;

FIG. 2 is a perspective view of a transverse section of the part of FIG. 1 together with a viewing window, and

FIG. 3 is a plan view of the inner surface of part of the viewing window.

In FIG. 1 a block 1 of electrically insulating material, has been moulded around a set of conducting cathode strips 2 which form one electrode set of a cross-bar addressing system and which are led through the sides of the block I in a vacuum-tight manner. The top face of the block 1 is provided with an array of cavities 3 which extend downwards as far as the strips 2. Thus part of a strip 2 is exposed in each cavity.

The top face of the block 1 is provided with two sets of parallel ridges 4 which extend in the length and width directions of the block I so as to separate the individual cavities 3 from each other.

FIG. 2 is a perspective view of a cross-section taken on the line Il-II of FIG. 1. A transparent viewing window plate 9 is sealed at 16 in a vacuum-tight manner to the top of a ridge provided round the periphery of the top of the block 1. The ridge is slightly higher than the ridges 4 so that a small gap of e.g., 25 m is present between the tops of the ridges 4 and the inner surface of the window plate 9 in order to allow the completed tube to be pumped and gas-filled in a uniform manner, The window plate 9 may be made of glass available under the type number 7059 Coming.

As an alternative soft glass may be used for the block 1. Thus the block 1 may be made of the material available under the Registered Trade mark Fusite H, a glass having an expansion coefficient suitably matched to nickel-iron if such material is used for the strips 2.

As an alternative the ridges 4 shown in FIG. 2 may be omitted.

FIG. 3 is a plan view of the inner surface of part'of the viewing window 9. On this inner surface is deposited an array of anode electrodes 10 of gold or nichrome. The array of anode electrodes corresponds to the array of cathode cavities 3. The anodes of each row of the array are each connected to a cross-bar supply conductor 11 therefore (which are also gold or nichrome) via an individual series resistor formed'as a meandering thin-film path 12 of electrically resistive material which may again be nichrome and which is deposited on the surface of the window 9. A supply wire or strip 14 is bonded to the termination of each anode supply conductor 11, which conductor may, if it is of nichrome, be gold plated during manufacture either completely or at its terminations only. The whole surface of the window 9 with its deposited layers is covered with a layer of electrically insulating material (not shown) such as evaporated silicon monoxide or R.F.- sputtered silicon dioxide except at the areas of the anodes l0 and the anode supply conductor terminations 13. If desired an individual transparent electrically conductive layer (not shown) such as nichrome may then be deposited on this insulating layer over part or the whole of each resistor 12 so as to contact the corresponding anode l0 and effectively increase the area thereof.

It is desirable that the anodes l0 and supply conductors ll be of low resistance. To achieve this, if the anode electrodes 10, the resistive paths 12 and the supply conductors 11 are each made of deposited nichrome, the conductive layers 11 may be several thousand A thick while the layers forming the electrodes 10 and the resistive paths 12 may be several hundred A thick. They may be made by coating the whole surface of the plate 9 by a layer of nichrome several thousand A thick, coating the terminations 13 with gold, etching these coatings by a photolithographic technique to leave the nichrome only at the locations of the anodes 10 and conductors 11, and nichrome/gold at terminations 13, coating the complete surface of the plate with a layer of nichrome hundred A thick, and etching this coating by a photolithographic technique to leave this nichrome only at the locations of the electrodes 10, the paths l2 and the conductors 11. The whole surface of the plate 9 with its nichrome layers may be coated with silicon monoxide or silicon dioxide about lp.m thick except at the extremities of the terminations l3 (i.e., up to a boundary 15), this silicon monoxide or dioxide then being etched only at the areas of the electrodes 10 by a photo-lithographic technique to expose these electrodes. The aforementioned individual conductive layers may then be deposited over each anode 10 and resistor 12.

If the resistive paths 12 are of nichrome several hundred A thick they may each be 40 mm long and have a width of 20am giving a resistance of each path of between 2 X 10 and 2 X 10 ohme depending on how the layers are deposited and the subsequently heating schedules used in assembling the panel. The electrodes 10 may each be in the form of a square of 0.3 mm side for an overall discharge cell size of 1.5 mm square, or of 0.1 mm side for an overall cell size of 1.0 mm square.

In a practical embodiment the cavities 3 were disposed in a rectangular array of the form shown in FIG. 2 but without the ridges 4. Each cavity was 0.8 mm square at its top tapering to 0.4 mm square at its base and the spacing between the cathode at the base of each cavity and the window plate 9 was 0.625 mm. The cavity depth was 0.6 mm. The cavities were 1.0 mm between centres (as were the anode electrodes 10 in order to correspond therewith).

After the window plate had been sealed all round to the top of the ridge extending around the top face of the block 1 so that each anode electrode 10 was positioned centrally over a cavity 3, the supply wires or strips 14 emerging through the sealing material in a vacuum-tight manner, the interior of the tube was evacuated through an exhaust tube (not shown) and was filled with a Penning gas atmosphere or pure neon at a pressure of several hundred Torr. The tube was then sealed off.

The completed tube was then aged by applying an operating potential between each cathode and anode supply conductor and continuing this application for several hours.

The application of an operating potential across each discharge path was found to result in the generation of negative-glow optical radiation in the resulting glowdischarge, the positive column part of the discharge being substantially or completely suppressed. Small anode glows were also often present due to the small anode areas.

In operation a positive potential of, e.g., 250V was applied to the supply wires or strips 14 relative to the cathode strips 2, this potential being above the maximum maintaining potential of glow-discharges in the cavities 3 (which may be e.g., 220V) but below the minimum striking potential thereof. An additional positive pulseof, e.g., 150V was then applied to each wire or strip 14 in'turn, the length of these pulses being sufficient to ensure that each anode-cathode discharge path in the corresponding row ignited. Thus each pulse length may be approximately l50p,sec. Immediately after each additional pulse (and before the application of the corresponding pulse to the next conductor 14) the potential at the corresponding conductor 14 was reduced to, e.g., 30V below its original potential for, e.g., l50p.sec. simultaneously with the application of positive-going pulses of, e.g., 30V to those cathode conductors 2 corresponding to the cross-points with the relevant conductor 14 where a discharge was not desired. Thus the potential at these cross-points was reduced momentarily to 190V (below their maintaining potential) and the corresponding discharges extinguished to leave only those desired. This was repeated for the remainder of the rows to build up the desired display.

The nichrome electrodes quoted are semitransparent and any glow discharge can be observed through them. Of course, even if the electrodes 10 were opaque, it would still be possible to observe the discharge through the gaps between adjacent turns of the resistive paths 12.

In the absence of the aforementioned individual conductive layers deposited over each anode l0 and resistor 12 it may be found that the silicon monoxide or dioxide layer over the surface of the plate 9 charges up in operation and thus gives rise to a time-lag in the operation of the tube. To counter this a highly resistive layer (having a resistivity of tens of thousands of ohms per square) may be deposited over the whole surface of the plate 9 after provision of the silicon monoxide or dioxide.

What is claimed is:

1. Electrical glow-discharge display device comprising an array of anode-cathode electrode pairs defining an array of individually addressable glow-discharge paths through a gas atmosphere contained in said device, and a cross-bar addressing system therefore, the anodes of each row of the array being individually connected through an electrically resistive connection to a common row supply conductor which forms part of the addressing system, the anodes, the electrically resistive connections and the row supply conductors being formed by thin films deposited on an inner surface of an optically permeable viewing window of the device,

and at least the major portion of the electrically resistive connections and of the row supply conductors being covered with an electrically insulating layer.

2. Display device as claimed in claim 1, wherein the insulating layer is substantially continuous over substantially the whole of said inner surface with the exception of breaks at each anode film.

3. Display device as claimed in claim 2, wherein an individual electrically conductive layer is deposited over the insulating layer which covers each electrically resistive thin-film connection, and said conductive layer electrically contacts the corresponding anode film.

4. Display device as claimed in claim 2, wherein each said electrically resistive connection comprises a meandering path of a film of an electrically resistive material.

5. Display device as claimed in claim 4, wherein said electrically resistive material is nichrome and said anodes and said row supply conductors are a nichrome film which is thicker than the film forming said electrically resistive connections.

6. A device as claimed in claims 1, the cathodes and column supply conductors therefore comprise elongate electrical conductors which extend through a block of electrically insulating material so that each elongate conductor is exposed at the base of each cavity of a column of cavities in a major surface of said block, the inner surface of said viewing window facing said major surface with the anode films aligned with the open ends of the cavities and spaced therefrom.

7. A device as claimed in claim 6, wherein each cavity tapers from its open end to Its base. 

1. Electrical glow-discharge display device comprising an array of anode-cathode electrode pairs defining an array of individually addressable glow-discharge paths through a gas atmosphere contained in said device, and a cross-bar addressing system therefore, the anodes of each row of the array being individually connected through an electrically resistive connection to a common row supply conductor which forms part of the addressing system, the anodes, the electrically resistive connections and the row supply conductors being formed by thin films deposited on an inner surface of an optically permeable viewing window of the device, and at least the major portion of the electrically resistive connections and of the row supply conductors being covered with an electrically insulating layer.
 2. Display device as claimed in claim 1, wherein the insulating layer is substantially continuous over substantially the whole of said inner surface with the exception of breaks at each anode film.
 3. Display device as claimed in claim 2, wherein an individual electrically conductive layer is deposited over the insulating layer which covers each electrically resistive thin-film connection, and said conductive layer electrically contacts the corresponding anode film.
 4. Display device as claimed in claim 2, wherein each said electrically resistive connection comprises a meandering path of a film of an electrically resistive material.
 5. Display device as claimed in claim 4, wherein said electrically resistive material is nichrome and said anodes and said row supply conductors are a nichrome film which is thicker than the film forming said electrically resistive connections.
 6. A device as claimed in claims 1, the cathodes and column supply conductors therefore comprise elongate electrical conductors which extend through a block of electrically insulating material so that each elongate conductor is exposed at the base of each cavity of a column of cavities in a major surface of said block, the inner surface of said viewing window facing said major surface with the anode films aligned with the open ends of the cavities and spaced therefrom.
 7. A device as claimed in claim 6, wherein each cavity tapers from its open end to Its base. 